The Bush administration moved forward on Friday with a program to expand collecting DNA samples from people in federal custody.

But it was unclear how federal laboratories would be able to handle the added work.

The Justice Department formally proposed regulations for collecting the samples, a technique that essentially mirrors taking the fingerprints of people arrested for federal offenses, as well as illegal immigrants detained by federal authorities.

The government now collects DNA just from felons. DNA, the genetic marker found in hair and blood and other body fluids, can provide a more concrete link to a crime than fingerprints, which often are not left at a crime scene or are difficult to collect.

For the new effort to succeed, the samples, most collected by swabbing an inside cheek, have to be entered into the DNA database of the F.B.I.

A spokeswoman for the bureau’s laboratory, Ann Todd, said it already had a backlog of 225,000 samples to be processed, a more complex procedure than entering fingerprints.

If Justice Department estimates are accurate, work at the laboratory would increase twelvefold, Ms. Todd said.

No additional money was provided for the laboratory when Congress authorized the new collection program in 2006.

Some advocates of the program have questioned whether the backlog will hamper it. In addition, the new regulations would give federal agencies discretion not to collect samples if that would tax their resources, further clouding the effectiveness of the program.

The Justice Department, which had worked on the regulations since last year, will write a final version after a 30-day comment period that began on Friday. Officials said they expected the collections to begin by Dec. 31. The department has estimated that 1.2 million people, a vast majority of them illegal immigrants who are not criminally charged, could fall under the regulations. That estimate, the department said, was based on the number of people whom federal agencies arrest and statistics from the Homeland Security Department.

A spokeswoman for the Homeland Security Department, Laura Keehner, said it was discussing with the Justice Department carrying out the regulations, specifically for illegal immigrants.

Although advocates for illegal immigrants condemned the DNA collection as an overreach by the government and potentially damaging to detainees or those who have been erroneously arrested, advocates for crime victims praised the program as another tool to catch killers and rapists. Thirteen states collect DNA from people under arrest.

Senator Jon Kyl, the Arizona Republican who pushed for the regulations, issued a statement applauding the Justice Department and citing the case of a man arrested in January in Chandler, Ariz., and linked to a half-dozen sexual assaults of girls.

The man, Santana Aceves, was deported in 2003, and Mr. Kyl said collecting Mr. Aceves’s DNA at that time might have prevented some of the assaults, which began in 2006.

The rules give agencies latitude to delay or not collect samples if, for example, sample kits are not available or if the collection impedes on “operational exigencies or resource limitations.”

Members of Congress have promised to address the problem by pushing for more money.

“I think it makes sense to expand the DNA database,” said Representative Adam B. Schiff, a California Democrat who has proposed a bill to increase money for DNA processing. “But if we are not going to provide the adequate resources, we are tremendously undercutting the whole effort.”